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Description of the DP Functions, Data, and Error Codes

DP Base Programming Interface for CP 5613/CP 5614

144

C79000-G8976-C108-01

4.3.1 Reading the Input Data of a DP Slave

Consistent Reading

There is a fixed data area in the process image of the CP 5613/CP 5614 for the

input data of each individual slave.

To allow the input data of a slave to be read consistently, your user program first

locks this data area to prevent it being updated by the DP master, then accesses

the area, and releases it again.

The program locks the area by writing the slave number to a control register in the

process image. The program releases the area by writing the value

DPR_DP_UNLOCK or a different slave number to the same register.

Example of Consistent Reading

"p" is a pointer to the process image that your user program obtained with the

"DP_get_pointer" call. Then 200 bytes of slave no. 5 are copied to a local buffer

"buf":

/* Lock the data area against updating */

p->ctr.D_lock_in_slave_adr = 5;

/* Copy data */

memcpy(buf, &p->pi.slave_in[5].data[0], 200);

/* Cancel lock again */

p->ctr.D_lock_in_slave_adr = DPR_DP_UNLOCK;

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Siemens SIMATIC NET PROFIBUS Manual de servicio Pagina 144